1. Field of the Invention
The present invention relates to circuit interrupters generally and, more specifically, to those kinds of circuit interrupters having a trip bar assembly that rotates during a tripping operation.
2. Description of the Prior Art
Molded case circuit breakers and interrupters are well known in the art as exemplified by U.S. Pat. No. 4,503,408 issued Mar. 5, 1985, to Mrenna et al., and U.S. Pat. No. 5,910,760 issued Jun. 8, 1999 to Malingowski et al., each of which is assigned to the assignee of the present application and incorporated herein by reference.
A continuing industry objective with respect to many types of circuit interrupters is to be able to reduce the size and/or footprint of the interrupter housing while at the same time providing the same or improved performance capabilities. A major advantage of creating such a "smaller package" is that it provides increased flexibility in installation. However, a consequence of this objective is that the internal space constraints of such interrupters have become much more limiting, posing certain design obstacles that need to be overcome.
Circuit interrupters include trip mechanisms that can be activated in a variety of manners so as to set in motion a tripping operation to open the contacts of the interrupter. These trip mechanisms often employ a rotatable trip bar assembly that, when selectively rotated, releases a portion of the operating mechanism to thereby generate a tripping operation.
Such circuit interrupters advantageously provide for automatic circuit interruption that causes the trip bar assembly to rotate when an overcurrent condition is sensed. This automatic interruption may be thermally, magnetically, or otherwise based. In addition, such circuit interrupters often enable a tripping operation to be manually initiated by implementation of a push-to-trip member which, when pressed, contacts and rotates the trip bar assembly.
Circuit interrupters may also advantageously have accessory devices, such as an undervoltage release (UVR) or a shunt trip, connected thereto. Such accessory devices can likewise initiate a tripping operation, and typically do so by contacting and rotating an accessory trip lever on the trip bar assembly that then causes the trip bar assembly to rotate. However, because of the required positioning and size of such an accessory trip lever, the lever sweeps through a relatively large range of motion within the circuit interrupter whenever any type of tripping operation occurs. Therefore, it is difficult to employ such an accessory trip lever within a circuit interrupter having the aforementioned internal space constraints. Internal components of such a circuit interrupter may obstruct the rotational movement of the accessory trip lever and undesirably prevent the trip bar assembly from sufficiently rotating in certain circumstances.
One problem associated with accessory trip lever obstruction is encountered when a bimetal is used to implement a thermal tripping operation. The bimetal reacts to current flowing therethrough, with the temperature of the bimetal being proportional to the current magnitude. As current magnitude increases, the heat buildup in the bimetal has a tendency to cause a bottom portion thereof to deflect (bend). When non-overcurrent conditions exist, this deflection is minimal. However, above a predetermined current level, the temperature of the bimetal will exceed a threshold temperature whereby the deflection causes the bottom portion to make contact with a thermal trip member of the trip bar assembly. This contact forces the trip bar assembly to rotate and generate a tripping operation.
Under certain circumstances, such as a short circuit condition or the presence of excessively high currents, the bimetal can quickly heat up to a higher temperature, causing the bimetal to deflect faster and to a greater extent than normal under overcurrent conditions. This enhanced deflection has a tendency to cause greater rotation of the trip bar assembly than what is necessary in order to generate a tripping operation, the movement of which can be hindered by the aforementioned obstruction of an accessory trip lever. Unfortunately, by preventing the trip bar assembly from continuing to rotate in this situation, an obstruction can prevent the bimetal from fully and properly deflecting, thereby undesirably causing the bimetal to "take a set." Such an event can destroy the calibration of the bimetal and prevent it from being properly calibrated thereafter.
Therefore, it would be advantageous if a way existed by which an accessory device tripping operation could be conveniently and effectively implemented within a circuit interrupter having internal space constraints. In particular, it would be advantageous if a way existed by which to accommodate for an aforementioned obstruction of an accessory trip lever while, at the same time, enabling the trip bar assembly to continue to rotate during a tripping operation.